1. Field of the Invention
The present invention generally relates to method and apparatus for cleaning a semiconductor wafer, and more particularly, an embodiment of the invention relates to a brush assembly for removing slurry particles from a semiconductor wafer.
2. Description of the Related Art
Integrated circuit fabrication typically includes a process step of creating an extremely flat surface on a surface of a semiconductor wafer. Chemical-Mechanical Polishing (CMP) is a known technique for planarizing the surface of a semiconductor wafer to a desired thickness. CMP typically involves contacting a polishing pad against the wafer and rotating the polishing pad with respect to the wafer. A slurry containing abrasive particles is typically applied to the surface of the wafer to facilitate mechanical polishing of the wafer. The slurry may also contain a chemical agent to increase the rate that material is removed from the wafer. After the wafer is treated in a CMP process, it may be scrubbed to clean the wafer surface of any remaining slurry particles. The wafer may be contacted with water to remove the slurry particles.
In one process, a brush assembly that includes a brush attached to a brush holder is used to clean a semiconductor wafer after a CMP process. The brush includes a backing plate comprising a plurality of holes disposed about the edges of the backing plate. The brush includes a surface for contacting the wafer located on a side opposite the backing plate. Water is passed through the openings in the backing plate to the portion of the brush that contacts the wafer surface during cleaning. The brush is connected to brush holder via a double-sided adhesive coupon placed between the backing plate and brush holder.
The brushes used in the above-described system need to be periodically replaced. Such replacement tends to be difficult and time-consuming. The old brush and the adhesive coupon must first be removed from brush holder. Removal of adhesive residue left by the adhesive coupon tends to be difficult, and acetone or another chemical often must be applied to brush holder to facilitate removal of the adhesive residue. Once the old brush and adhesive coupon are removed, a new double-sided adhesive coupon is placed on the brush holder. Backing paper usually must be peeled from both sides of the adhesive coupon to expose its adhesive surfaces. Occasionally, the adhesive coupon tears when the backing paper is peeled away. The adhesive coupon contains a number of openings arranged to match a pattern of openings on the brush holder and the backing plate of the brush. It tends to be difficult to position the adhesive coupon on the backing plate and/or brush holder such that the openings in the backing plate, brush holder, and adhesive coupon are properly aligned. In addition, the adhesive coupon may be incompatible with cleaning agents (e.g., ammonium hydroxide) that reduce or eliminate the adhesive capability of the adhesive coupon.
The brushes are typically replaced by operators who must wear latex gloves, which increases the difficulty and time required to: (a) remove the backing paper from the adhesive coupon without tearing the coupon, and (b) properly position the adhesive coupon on both the backing plate and the brush holder such that the patterns of openings are aligned in each of the three components. An operator typically spends about 2-4 hours to replace 6 of the brushes.
Another problem with some wafer brushes involves the application of cleaning fluid to the brush and wafer. The brush is usually made from a flexible, porous sponge-like material. One side of the brush is designed to contact the surface of a semiconductor wafer. The other side of the brush it is attached to a backing plate. The backing plate may include a plurality of holes opened to the upper surface of the sponge-like brush. A cleaning fluid may be applied to the top of the backing plate in order to pass through these holes and soak into the brush and onto the surface of the semiconductor wafer. If the cleaning fluid is applied while the brush is rotating, much of the cleaning fluid flies off of the brush backing plate instead of flowing into the holes and soaking through the brush. Therefore, it may be necessary to stop rotation of the brush to apply the cleaning fluid or to change the cleaning fluid composition and then restart brush rotation.
Often it is desirable to change or cycle the composition of the cleaning fluid from one fluid to another or to introduce different chemicals into the cleaning fluid. To avoid the fluid from flying off the brush and to allow the fluid to soak into the brush and reach the wafer, brush rotation may need to be stopped each time the cleaning fluid is changed or cycled. This starting and stopping of brush rotation decreases the overall throughput of the wafer cleaning process. Furthermore, the cleaning fluid cannot be applied to the wafer at a very fast rate. The rate which cleaning fluid may be applied to the wafer is limited to the amount of cleaning fluid that can pass through the backing plate openings and soak through the sponge-like brush. In some circumstances a greater flow rate of cleaning fluid may be desirable.
Yet another problem results when the wafer brush is removed from the surface of the semiconductor wafer. Particles may become trapped in the porous holes within the lower surface of the sponge-like brush. The flow rate of cleaning fluid passing through the brush may not be great enough to dislodge these particles. As the brush is lifted from the surface of the semiconductor wafer, surface tension between the cleaning fluid on the surface of the wafer and the sponge pores may cause those particles to be sucked from the brush and left upon the surface of the semiconductor wafer. This results in an undesirable amount of particles being left on the surface of the wafer, thus requiring additional cleansing steps to remove the particles.
It is therefore desirable that an improved brush assembly be derived for cleaning a semiconductor wafer.